Lipases have been widely used for ester synthesis reactions between various carboxylic acids such as fatty acids and alcohols such as monoalcohols and polyols, transesterification reactions between alcohols and carboxylic acid esters, between carboxylic acids and carboxylic acid esters, and between multiple carboxylic acid esters, and the like. Of these reactions, the transesterification reactions are an important technology as methods for producing esters of various fatty acids, sugar esters, and steroid esters, including those for modification of animal or vegetable fats and/or oils. When a lipase, which is a fat and/or oil hydrolyzing enzyme, is used as a catalyst for such a reaction, the transesterification reaction can be carried out under a mild condition of about room temperature to approximately 130° C. In this case, the side reactions are more suppressed and the energy costs are more reduced than in a conventional chemical reaction. Moreover, the lipase used as the catalyst is highly safe, because the lipase is a natural product. Furthermore, because of the substrate specificity and the positional specificity, the target product can be produced efficiently.
Since such a lipase is expensive, attempts have been made to stabilize the enzymatic activity of a lipase by activating the enzymatic activity of the lipase and suppressing decrease in activity of the lipase. For example, before a transesterification of a raw material fat and/or oil is conducted by using a lipase, the raw material fat and/or oil is treated with a substance having amino groups such as an anion exchange resin. In this manner, the decrease in enzymatic activity has been suppressed (Patent Literature 1). In addition, in Patent Literature 1, the raw material fat and/or oil and a clay are brought into contact with each other at 110° C. in a decolorization step. However, this step is intended only for decolorization of the fat and/or oil, and not for suppression of decrease in enzymatic activity. In addition, when the fat and/or oil and the clay are brought into contact with each other at 110° C., the enzyme cannot be activated. As described above, no study has been made to stabilize the enzymatic activity by bringing a raw material fat and/or oil and a clay into contact with each other before a transesterification reaction.